The overall goal of this investigation is to improve the diagnosis of hearing loss and central auditory deficits in young children. The use of certain auditory evoked potentials (AEPs), including middle latency (MLR) and late potentials, has been limited in pediatric populations because of the variability of these responses during sleep or the dependence of the responses on a behavioral task which may be beyond the capabilities of a young child. This project is an investigation of the MLR and mismatch negativity (MMN) AEPs in children and addresses how these limitations may be overcome. The first major aim is to develop a means to identify the periods during sleep that are favorable for recording the MLR. Previous research has indicated that certain sleep stages are more favorable than others and that they may be distinguished by analyzing the EEG for specific amplitude and frequency characteristics. Proposed is an investigation of the utility of the "delta ratio", a measure of the dominance of delta activity in the EEG. On-line detection of delta presence/absence could signal a clinician or researcher when a child is in a favorable MLR recording period. Similar measures could eventually be applied to other AEPs. A second major aim is to characterize the MMN in response to well-defined speech stimuli to determine if this response can provide an objective neurophysiologic measure of auditory discrimination in school-aged children. The MMN reflects central auditory processing of small acoustic differences and does not depend on active participation from the child. The MMN will be elicited by synthesized speech stimuli that differ in acoustic parameters that are fundamental to speech perception. Another objective is to determine whether developmental changes in the MLR and the MMN correlate with behavioral measures of development as determined by standardized measures of mental aptitude and processes underlying learning and academic achievement. Clinical applicability of the combined electrophysiologic/behavioral approach will be evaluated in (1) children with behaviorally identified central auditory deficits and (2) children with attention deficit hyperactivity disorder -- a group in which the co-existence of auditory processing deficits is well established.